Microbiology Flashcards
What colour to Gram Positive organisms stain on a Gram Stain and why?
PURPLE. They stain well due to thick peptidoglycan layer.
Do gram positive organisms produce endotoxin or exotoxin?
Exotoxin which is exported from the cell
What are streptococci? How are they arranged?
Gram postitive aerobic cocci in strips
What is alpha-haemolysis and which organisms cause it?
Partial haemolysis. Caused by Strep. Pneumoniae and Strep Viridans.
What is beta-haemolysis and which organisms cause it?
Complete haemolysis. Caused by group A and group B strep
What is gamma-haemolysis and which organisms cause it?
No haemolysis. Caused by enterococcus
What are staphylococci? How are they arranged?
Gram positive aerobic cocci in clusters
What organisms are coagulase positive?
Staph.Aureus (wound + skin infections)
What organisms are coagulase negative?
All other staph, e.g. skin commensals
Name an aerobic gram positive bacilli
Bacillus cereus (food poisoning from rice)
Name an anaerobi bacilli
Clostridium Difficile (Antibiotic associated colitis)
What colour do gram negative organisms stain a gram stain and why?
PINK. Stain less well as thinner peptidoglycan layer doesn’t retain stain well
Do gram negative organisms produce endotoxin or exotoxin?
Endotoxin. It is part of the cell wall.
Which gram negative organisms are strict aerobes?
Legionella
Pseudomonas
Name 2 gram negative diplococci
Neisseria gonorrhoea
Neisseria meningitides
What are the gram negative gut commensals?
E.Coli
Klebsiella
Proteus
What are the gram negative gut pathogens?
E.Coli 0157
Salmonella
Shigella
What toxin does E.Coli 0157 produce and what can it cause?
VEROTOXIN. Causes haemolytic uraemic syndrome. Commonest cause of renal failure in kids under 5
Name a strict anaerobic gram negative Bacilli
Bacteroids
What gram negative organism causes whooping cough?
Bordetella Pertussis
What gram negative organism causes COPD exacerbations?
Haemophilus Influenza
What does bacteriostatic mean?
An antibiotic which inhibits cell growth
What does bactericidal mean?
An antibiotic which kills bacteria directly
Which classes of antibiotic work on the cell wall?
Penicillins
Cephalosporins
Glycopeptides
